1. Field of the Invention
The present invention relates generally to power supplies, and more specifically to a method and apparatus for adaptively controlling power supplied to a hot-pluggable subsystem.
2. Background of the Invention
Computers and other electronic systems such as telecom systems require replacement and/or addition of subsystems without removing power from a host system. Known as “hot-pluggable” subsystems, these electrical devices must operate properly after connection and disconnection, while not disrupting the operation of other electronic circuits. Telecom systems typically operate at a much higher voltage (−48V) and telecom subsystems typically have high current drains due to the low-impedance nature of telephony circuits. Thus, the input capacitances required to filter EMI and conducted ripple on the input of telecom subsystems are typically large and a hot-pluggable subsystem for telecom generally requires sophisticated inrush current protection.
Additionally, peripheral devices, storage devices and redundant processor modules in both network server systems and personal computing systems can be removed or attached while the systems remain active. Network connections between systems must also support active connection and disconnection, since the entire network should not be shut down to add or remove computers or other devices. Power to connected sub-systems may be supplied through network interface cables. For example, the Powered Ethernet Specification 802.3 promulgated by the Institute of Electrical and Electronic Engineers (IEEE), specifies an interface wherein power is supplied through the network cable connection. Hot-pluggable network hubs, network telecom cards including fiber optic interfaces, transceivers and cards for analog telephonic interfaces may all be powered by a host system.
Inrush current must be managed in hot-plugging systems, as the transients generated when the hot-pluggable subsystem is connected to the host system can damage connectors, cause dips in the power supply rails and generate electromagnetic interference (EMI) that affect the operation of the host system and other connected subsystems.
Power supplies for hot-pluggable subsystems having a minimum of electrical connections and incorporated within small integrated circuit packages are very desirable. In general it is useful to provide power supply integrated circuits requiring a minimum of circuit area and external connections. Generally, an external pass element is used with an integrated circuit controller so that the controller may be used in many different applications with the pass element sized appropriately for the current and voltage requirements of a particular application. As the size and the equivalent input capacitance of the pass element used is not known a priori, therefore it would be desirable to compensate for differences in the size of the pass element in order to normalize turn on time and other characteristics without requiring external components specifically chosen for a given pass element.
Power supplies for a hot-pluggable subsystem are typically required to provide a stable time period in which the power supply voltage applied to the hot-pluggable device does not vary while the hot-pluggable device initializes. This presents difficulty in that mechanical contact bounce may electrically connect and disconnect the power supply conductors several times before the device is properly coupled. A de-bounce time interval and/or a power-on-reset (POR) time interval are typically provided to prevent improperly initializing a hot-pluggable subsystem, but implementation of the de-bounce and power-on-reset time intervals typically requires additional components, adding to size, complexity and cost of power supply electronics.
Other features desirable in a power supply for coupling to a hot-pluggable sub-system are short-circuit protection (or current limiting) to prevent misalignment or accidental shorting of the power supply pins from damaging the power supply or hot-pluggable subsystem. Short-circuit protection differs from inrush current protection in that short-circuit protection must distinguish from a transient short-circuit type load (virtual AC short circuit) that is produced by the large input capacitors of hot-pluggable subsystem power supplies or bypass capacitors. The pass device used in a hot-pluggable power supply can fail or be degraded in operating characteristics and reliability if a short circuit is placed across the output terminals of a hot-pluggable power supply.
Typically, implementation of short-circuit discrimination vs. current limiting requires additional complexity within the power supply control circuits and additional components to set operating levels, etc. Large capacitors are required to prevent startup transients from turning on the pass device through the parasitic capacitances of the pass device. Short-circuit protection circuits as well as current limiting circuits are generally desirable with an auto-restart feature so that input power does not have to be removed in order for the hot-pluggable power supply to recover from the protection conditions. Auto-restart circuits typically require external timing components, and due to the long time constants desired, auto-restart circuits typically use large capacitors.
Under-voltage lockout (UVLO) protection is also desirable in hot-pluggable systems, so that the hot-pluggable sub-system power supply does not produce an output until the power supply input has reached a minimum voltage level.
Therefore, it would be desirable to provide an improved method and system for adaptively controlling power supplied to a hot-pluggable subsystem. It would be further desirable to control power supply current during initialization and mechanical contact bounces without requiring additional timing components, external connections and external components to support operational features. It would be further desirable to provide an auto-restart capability after a short circuit has been detected across a load, without requiring additional components or external circuit connections.
It would additionally be desirable to incorporate UVLO protection and turn-on short-circuit protection without requiring additional external connections. It would further be desirable to provide the above-mentioned features within a small integrated circuit package having a minimum of electrical connections.